Note 9 - Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Stockholders' Equity Note [Abstract]

Schedule of Potential Per Share Dividend Amounts Quarterly Price Levels [Table Text Block]

Quarterly average realized silver price per ounce		Quarterly dividend per share		Annual dividend per share
	$30		$0.01		$0.04
	$35		$0.02		$0.08
	$40		$0.03		$0.12
	$45		$0.04		$0.16
	$50		$0.05		$0.20
	$55		$0.06		$0.24
	$60		$0.07		$0.28

Schedule of Dividends Payable [Table Text Block]

	(A)		(B)		(C)		(A+B+C)
Declaration date	Silver-price- linked component per share		Minimum annual component per share		Special dividend per share		Total dividend per share		Total dividend amount (in millions)		Month of payment
February 25, 2013	$	—	$	0.0025	$	0.01	$	0.0125	$	3.6	March 2013
May 10, 2013	$	—	$	0.0025	$	—	$	0.0025	$	0.7	June 2013
August 8, 2013	$	—	$	0.0025	$	—	$	0.0025	$	0.9	August 2013
November 5, 2013	$	—	$	0.0025	$	—	$	0.0025	$	0.9	December 2013
February 21, 2014	$	—	$	0.0025	$	—	$	0.0025	$	0.9	March 2014
May 5, 2014	$	—	$	0.0025	$	—	$	0.0025	$	0.9	June 2014
July 31, 2014	$	—	$	0.0025	$	—	$	0.0025	$	0.9	September 2014
November 5, 2014	$	—	$	0.0025	$	—	$	0.0025	$	0.9	December 2014
February 17, 2015	$	—	$	0.0025	$	—	$	0.0025	$	0.9	March 2015
May 6, 2015	$	—	$	0.0025	$	—	$	0.0025	$	0.9	June 2015
August 6, 2015	$	—	$	0.0025	$	—	$	0.0025	$	0.9	September 2015
November 3, 2015	$	—	$	0.0025	$	—	$	0.0025	$	0.9	December 2015
February 20, 2016	$	—	$	0.0025	$	—	$	0.0025	$	0.9	March 2016

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

	Shares			Weighted Average Grant Date Fair Value per Share
Unvested, January 1, 2015		2,235,575		$	3.31
Granted		2,171,713		$	2.44
Canceled		(32,587	)	$	2.99
Distributed		(998,903	)	$	3.38
Unvested, December 31, 2015		3,375,798		$	2.73